Run Unit tests on windows (and possible Mac)

[jonvanausdeln]

Currently, we run unit tests on Ubuntu only in CI.

We do now have some unit tests that seem to only work on Windows due to some upstream choices (#9886)

We should consider running them on windows as well. This might uncover some unit test failures we haven't seen before and might have to deal with.

[jennybc]

Adding a bit more color as requested by @jonvanausdeln. While developing #9886, I saw 2 unit test failures that I first thought were legit. But upon further investigation, it turns out the isUNC() path utility returns false on non-Windows:

positron/src/vs/base/common/extpath.ts

Lines 122 to 125 in 13c48a0

	if (!isWindows) {
	// UNC is a windows concept
	return false;
	}

Therefore, these unit tests only provide good data when run on Windows. And yet we don't seem to run unit tests on Windows (yet).

This anecdote serves as an example of why we might want to run unit tests on Windows. For now, I'm skipping these particular tests on not-Windows, which probably means these tests effectively don't run.